Radially expandable devices are utilized in a wide range of applications, including a number of biological applications. Radially expandable devices in the form of inflatable balloons have been proposed for treatment of body passages occluded by disease and for maintenance of the proper position of catheter delivered medical devices within such body passages. Such expandable devices can be constructed of elastomeric materials such as latex.
A number of general problems are associated with such elastomeric balloons. Balloons and other expansion devices constructed of elastomeric materials can lack a maximum inflation or expansion diameter in that the prolonged application of an inflation medium will cause the balloon to continuously expand until the balloon bursts. Thus, over inflation of an elastomeric balloon may result in damage to the body vessel or organ being treated or may result in the balloon bursting within the body. Elastomeric balloons frequently do not inflate symmetrically and may not inflate to the desired size and shape. Asymmetrical expansion, as well as failure of the balloon to properly inflate, can lead to incomplete treatment of the body vessel. The high coefficient of friction of most elastomeric materials, such as latex, polyurethane, or silicone rubber, can result in damage to one or more cellular layers of the wall of the body vessel or organ being treated. Additionally, elastomeric expansion devices generally have insufficient strength for a number of applications, such as compressing adherent thrombus deposits formed on vascular walls and centering the catheter shaft away from the vessel wall.
Some elastomeric balloons include the feature of delivery of a liquid, such as a drug, to a targeted location. However, conventional balloons lack the ability to selectively control the rate of liquid passing through the walls of the balloon to the desired location within the patient. For example, the balloon can include a plurality of holes to allow a liquid inflating the balloon to pass through the balloon walls and be applied to a targeted location. However, if the balloon is required to be at full inflation to apply pressure to walls of a body lumen, the liquid used to inflate the balloon will pass through the plurality of holes at an increased rate, which may be undesireable.
Some applications of catheter balloons have incorporated design elements to permit an increased flow rate. One example is the use of a contrast agent injected into a lumen for aiding in radiographic viewing of a targeted location. Pressurized injections for viewing lumens, such as tubular vascular conduits, were subject to rapid washout and loss of the radiographic picture because of blood flow through the injected area. These catheters and injection systems were developed to permit for rapid bolus injections for diagnostic or therapeutic purposes. They were often utilized to obtain better visualization of structures, lesions, and narrowed areas, and allowed improved diagnostic information to be obtained.
More recently, improved imaging technology has enabled a number of viewing techniques, such as digital subtraction, advanced contrast, and lowered requirements for x-rays and exposure. In turn, more complete pictures, with improved resolution, have been obtained with less contrast media being introduced to the target location.
However, such advances have not yet adequately addressed the issue of introducing contrast media to view small, diseased or damaged, vessels, that are either in areas that are difficult to access, or are minor branches from larger flowing vessels.